Methylthioadenosine phosphorylase (MTAP) is a key enzyme in the methionine salvage pathway whose function is to convert 5cent-deoxy-5cent-methylthioadenosine (MTA) into methionine. Inactivation of MTAP, generally by homozygous deletion, is found in both solid and hematologic malignancies at a high frequency. Because MTAP is located near the CDKN2A/ARF tumor suppressor gene, it is unclear if loss of MTAP plays a primary role in tumorigenesis or if it is lost simply due to proximity to CDKN2A/ARF. In published work and preliminary data presented here, we show that reintroduction of MTAP into MTAP-deleted tumor cell lines significantly suppresses tumorigenicity and affects processes involved in cell migration and invasion. We also found that mice heterozygous for a MTAP null allele (MtaplacZ) die prematurely of lymphoproliferative disease resembling T-cell lymphoma. Taken together, these data suggest that MTAP loss plays a functional role in the development of cancer. The overall goal of this proposal is to determine how MTAP loss contributes directly to the development of cancer. There are four specific aims. In the first aim, we will determine if germline mutations in MTAP accelerate tumorigenesis in mice. We will fully characterize the lymphoproliferative disease in MTAP heterozygous animals and determine if they have full fledged lymphoma. We will also determine if MTAP loss can accelerate tumorigenesis in two different mouse models. In the second aim we will determine if pharmacologic inhibition of MTAP can cause or enhance tumorigenesis in mice using the recently developed transition state inhibitor MT-DAD-Me-ImmA. Using this compound we will test the hypothesis that inhibition of MTAP will accelerate the development of tumors both in normal and CDKN2A/ARF deficient mice. In the third aim we will determine the effect of MTAP loss on invasion and metastasis in vivo. We will inject fluorescently labeled isogenic cell lines into SCID mice and use state-of-the-art in vivo whole body imaging to determine how MTAP expression affects invasion and metastasis. Finally in the last aim we will test the hypothesis that MTAP-loss affects tumorigenesis by altering gene expression via accumulation of MTA that inhibits methyltransferase enzymes regulating chromatin and gene expression. These studies are significant because an understanding of the role that MTAP deletion plays in tumorigenesis may lead to novel therapeutic strategies for MTAP-deleted tumors. In addition, these studies will establish how a house-keeping metabolic enzyme can have a novel role as a tumor suppressor gene.